Tail Kit

I was able to spend some time last night and today getting the front spar riveted, then the in-spar ribs and stringers. I was happy with my riveting, although I did end up drilling a couple where the bucking bar slipped and malformed the shop head. By the end of the day I think I’d set about 300 rivets, with about the same number to go to finish the Horizontal Stabilizer. This has been very good riveting practice, I’m definitely producing more consistently good rivets, and I’m moving much faster. Most of the remaining rivets are around the edges and for the most part, can be squeezed. I’ll probably squeeze them, because it’s faster and quieter, which helps when it’s late at night.

The black scuff marks in this picture are from black electrical tape on the bucking bar, rubbing on the spar and ribs. The tape is to stop the bar from scratching the aluminum.

Slowly the clecos are coming out and the rivets are going in. Each time I lift and turn the whole assembly, it’s noticeable how much lighter it’s getting. Clecos are much heavier than rivets!

I applied some primer to the countersunk holes on the flanges of the spars and stringers. This is to provide a barrier between the spars and the dimpled skin where the skin will sit inside the countersunk hole. I sprayed some rattle-can primer into a plastic cup, then used a cotton bud to apply it to the holes. The primer color is olive drab, but it will be completely covered so I’m not worried about it not matching the white primer I used on the rest of the parts.

Then I inserted the forward spar into the skins, and riveted the spar to the nose ribs, joining the whole forward spar and rib assembly to the skins. I couldn’t get my pneumatic pop rivet tool into the rather narrow gap between ribs, so I used my hand squeezer to set the rivets. Everything came out nicely.

Here’s the clecoed skins, ready for the next step of setting the 600 odd rivets.

I also applied some thread paint to the torqued bolts on the rear spar. This will provide a visual reference to identify if the nuts ever loosen up for any reason.

I finished up the riveting of the nose ribs, and then drilled and removed one particularly ugly rivet. My riveting woke up one of the kids a couple of times, so I’ll need to finish the one final rivet tomorrow.

Didn’t make much progress over the weekend, but I set up the cradles and skins, then started riveting the nose ribs to the skins. It’s been a while since I bucked rivets, as most of the rudder was done with the squeezer, back riveting, or pop rivets. I made a practice piece to remind myself how to do it, and to ensure I had the right air pressure at the gun. Access is a bit awkward, especially for the forward most rivets. The skins are deep enough where it’s a stretch getting a hand down inside, and near the leading edge, there’s not enough room for a hand, a bucking bar, and a rivet. I finished this step on one skin, getting the three nose ribs in (the 4th one is attached to the spar and gets riveted in later), and started on the second. I’ve got a few rivets that will need to be drilled out and redone, but I’ll worry about that once I have the whole step completed. I may end up using flush pop rivets in the forward rivet holes, since it’s hard getting a bucking bar on those rivets, and I managed to mess up a few of them.

The forward-most rivets in this rib are both bent and not fully formed. I’ll drill out and replace:

I riveted the stringers to the in-board in-spar ribs and stringer web.

Then I clecoed and riveted all of the in-spar ribs to the front spar, and the two outside nose ribs. I got everything done with the pneumatic squeezer, which was easy given that I have a sheet with all the settings. Just twist the adjustable set the right number of turns and then squeeze away. These were all 4-4 rivets except for 8 4-5 rivets where the rivets go through the spar, spar cap, and then the rib.

Next step is to start riveting the nose ribs to the skins.

I finished up the Spar and stringer countersinking work tonight, everything went quite well. The only issue I had was when I tried to use the drill press for the stringers. After a lot of setup time, and lots of clamping, the piece moved slightly and I ended up with a lopsided hole. I switched back to using the drill after that mistake, as it’s easier to feel what’s happening and stop or adjust if needed. The enlarged hole will need to be drilled out to fit a larger rivet, which shouldn’t be a problem. Given that I countersunk over 400 holes, I’m ok with one error.

Then I riveted the inboard inspar ribs to the stringer web, and clecoed the stringers to the stringer web. I decided to stop there, as it’s getting late.

More countersinking on the Horizontal Stabilizer spars tonight. I finished the rear spar, and got about half way through one side of the forward spar. It’s getting faster, given how much practice I’m getting, but I think I still have another hour to go to finish this step.

I finished deburring and dimpling the HS skins this weekend, and started countersinking the spar flanges where they will accept the dimples. It’s challenging getting a perfect countersink. The goal is to have the top of a rivet be 0.007 inches below flush. Even with a well calibrated countersink, just the slightest hand pressure difference can result in a different amount. I contemplated setting up the drill press, but opted for the hand drill where I can more easily feel what’s happening. The drill press would also be a little awkward given how long the spars are (10 feet). Everything came out ok so far, I’ve finished around 50 of ~400 holes. Once I’m done countersinking I’ll also prime the inside of these holes, as they will be contacting the skins.

The last couple of nights I’ve spent time deburring and dimpling the HS skins. I peeled off the vinyl inside the skins, and on the outside to expose the holes. Deburring is fairly easy, the edges don’t take much to smoothen out, and the holes are all pre-punched to final size. For the holes, a quick debur with the tool is all I’m doing. For edges, I’m using my vixen file to remove bumps, then an edge deburrer, and then a small file. The combination of tools gives a good outcome. I was only able to finish dimpling one side of one skin tonight, I just can’t stay awake any longer.

Tonight I started by addressing an over-sunk hole on the spar. I reamed the hole out to #30 size, then countersunk for a 1/8th rivet. Then I trimmed a 4-5 rivet to 4-4.5, and riveted it in place. This is the very middle rivet on the top of the spar, so it even looks symmetrical.

Then I used a beam-style torque wrench to torque the rear spar nuts to 28 inch pounds. The tool is easy to use for these low torque settings, and apparently sufficiently accurate.

Then I match drilled some holes for the inboard most ribs, then dimpled all the ribs, except for the specific holes that will take screws for the fairings etc.

Here is the forward spar with the inboard ribs clecoed on for match drilling. They are set at a 10 degree angle:

I used the squeezer to dimple the ribs. It was fast and easy.

Stack of dimpled ribs: